大尺寸的 HashSet 抛出 StackOverflow 错误

Question

I have 81K records of Long object and I am trying to store it in HashSet. My code snippet looks like this:

private static HashSet<Long> hashSet = new HashSet<>(Arrays.asList(*81K records*));

While compiling this is giving me StackOverflow Error . I am not understanding why only 81K records are being problem here? Solutions are appreciated.

Java version. :

openjdk version "1.8.0_322"
OpenJDK Runtime Environment Corretto-8.322.06.1 (build 1.8.0_322-b06)
OpenJDK 64-Bit Server VM Corretto-8.322.06.1 (build 25.322-b06, mixed mode)

Stack Trace:

[javac] 
    [javac] 
    [javac] The system is out of resources.
    [javac] Consult the following stack trace for details.
    [javac] java.lang.StackOverflowError
    [javac]     at com.sun.tools.javac.code.Type.map(Type.java:220)
    [javac]     at com.sun.tools.javac.code.Type.map(Type.java:220)
    [javac]     at com.sun.tools.javac.code.Type.map(Type.java:220)
    [javac]     at com.sun.tools.javac.code.Type.map(Type.java:220)
    [javac]     at com.sun.tools.javac.code.Type.map(Type.java:220)
    [javac]     at com.sun.tools.javac.code.Type.map(Type.java:220)
    [javac]     at com.sun.tools.javac.code.Type.map(Type.java:220)
    [javac]     at com.sun.tools.javac.code.Type.map(Type.java:220)
    [javac]     at com.sun.tools.javac.code.Type.map(Type.java:220)
    [javac]     at com.sun.tools.javac.code.Type.map(Type.java:220)
    [javac]     at com.sun.tools.javac.code.Type.map(Type.java:220)
    [javac]     at com.sun.tools.javac.code.Type.map(Type.java:220)
    [javac]     at com.sun.tools.javac.code.Type.map(Type.java:220)
    [javac]     at com.sun.tools.javac.code.Type.map(Type.java:220)
    [javac]     at com.sun.tools.javac.code.Type.map(Type.java:220)
    [javac]     at com.sun.tools.javac.code.Type.map(Type.java:220)
    [javac]     at com.sun.tools.javac.code.Type.map(Type.java:220)
    [javac]     at com.sun.tools.javac.code.Type.map(Type.java:220)
    [javac]     at com.sun.tools.javac.code.Type.map(Type.java:220)
    [javac]     at com.sun.tools.javac.code.Type.map(Type.java:220)
    [javac]     at com.sun.tools.javac.code.Type.map(Type.java:220)
    [javac]     at com.sun.tools.javac.code.Type.map(Type.java:220)

Line 220 of Type :

 208     /**
 209      * Return the least specific subtype of t that starts with symbol
 210      * sym.  If none exists, return null.  The least specific subtype
 211      * is determined as follows:
 212      *
 213      * <p>If there is exactly one parameterized instance of sym that is a
 214      * subtype of t, that parameterized instance is returned.<br>
 215      * Otherwise, if the plain type or raw type `sym' is a subtype of
 216      * type t, the type `sym' itself is returned.  Otherwise, null is
 217      * returned.
 218      */
 219     public Type asSub(Type t, Symbol sym) {
 220         return asSub.visit(t, sym);
 221     }
 222     // where
 223         private final SimpleVisitor<Type,Symbol> asSub = new SimpleVisitor<Type,Symbol>() {

Answer 1

The specific issue is that Java type inference cannot deal with such a long constant -- as reflected by the stack overflow you got in the Java compiler itself -- but it's also the case that Java bytecode format does not allow you to put such large amounts of data into your source code. The maximum size of the code for a method -- which is how Java initializes this behind the scenes -- is 64KB; storing 81K long constants alone is 10 times more than this limit.

You can certainly store this data into a HashSet and the like, but you must load it at runtime from a file.

Answer 2

The HashSet is irrelevant here. The problematic part is the varargs invocation of Arrays.asList with 81,000 elements.

To reproduce the issue, we can use the following code

class Tmp {
  static final String ARGUMENTS = "<<INSERT ARGUMENTS HERE>>";

  static final List<String> TEMPLATE = Arrays.asList(
      "import java.util.Arrays;",
      "import java.util.List;",
      "",
      "class Tmp {",
      "  static final List<Integer> L = Arrays.asList(",
           ARGUMENTS,
      "  );",
      "}");

  public static void main(String[] args) throws IOException {
    Path p = Files.createTempFile("Test", ".java");
    Files.write(p, () -> TEMPLATE.stream()
        .flatMap(line -> line.equals(ARGUMENTS)? varargsArgument(): Stream.of(line))
        .iterator());
    JavaCompiler c = ToolProvider.getSystemJavaCompiler();
    c.run(System.in, System.out, System.err, p.toString());
  }

  static Stream<CharSequence> varargsArgument() {
    return IntStream.range(0, 8100).mapToObj(i -> IntStream.range(0, 10)
            .mapToObj(j -> i * 10 + j + (i < 8099 || j < 9? ", ": ""))
            .collect(Collectors.joining()));
  }
}

With OpenJDK 8 , it produces the

java.lang.StackOverflowError
    at com.sun.tools.javac.code.Type.map(Type.java:220)
   …

On recent JDKs, eg JDK 12 , it produces

/tmp/Test14992292170362927520.java:6: error: code too large
  static final List<Integer> L = Arrays.asList(
                             ^

showing that even when the compiler bug has been fixed, such code can't get compiled.

Such amount of data should be included as embedded resource which you read in once at startup.